Comparison of TDM and OFDMA access methods for powerline OFDM systems

In OFDM systems deployed over noisy in-home powerline channels, with extraneous interference sources, the capacity of different carriers or tones across the frequency spectrum, varies significantly between different outlet pairs (OPs). OFDMA (joint frequency and time access) can be used to exploit this variation by scheduling only "good tones" for a link and thereby may be expected to provide higher system capacity than TDMA, but at the cost of higher implementation complexity. This paper studies the capacity and coverage for TDMA and OFDMA over powerline channels. Two OFDMA schedulers are proposed. The system capacity and service availability (coverage) are computed using these schedulers, and compared to those of a TDMA scheduler, for HDTV streaming applications. The powerline channels in apartments and IDUs are characterized by empirical measurements made using an FFT-OFDM PHY. OFDMA provides capacity and utilization improvements over TDMA in several cases where the OPs exhibit significant variations in performance of different tones.